The present invention is directed to apparatuses for providing read signals for information processing devices. The present invention is particularly useful with preamplifier (preamp) read signal providers for reader apparatuses associated with hard disc drives in computers and similar products.
Preamp reader output common mode voltage (read signal) often changes significantly in different modes of operation of the preamp devices. For example, a reader common mode voltage output signal commonly spikes or varies when the preamp reader device changes operating modes, such as when changing from a normal read mode to a non-read mode. Such sharp variations in value of common mode voltage output signal require that the signal be permitted to settle before it is useful in information conveying operations. That is, perturbations and deviations must settle or damp to within acceptable limits in order that information conveyed by the output signal may be regarded as accurate. Time required for settling or damping such perturbations is time during which an information processing device using the reader output signal cannot operate. That is, read time is lengthened and response time is longer. In the present marketplace that requires ever faster response times a need for such settling is a waste of capacity if it can be avoided.
One significant source of such perturbations, and their consequent required settling time, has been rooted in a failure to maintain reader common mode voltage output signals at substantially constant levels in various modes of operation of preamp devices. That is, while common mode voltage output signals are maintained level during read mode operations, during non-read mode operations prior art apparatuses only kept the common mode voltage output signals from rising above a predetermined limit. There was no prevention against the output voltage signal's reducing in value. As a consequence, when a preamp device configured according to the prior art was in a non-read mode, the common mode voltage output signal was kept below a predetermined value, but often drifted to a lower value than was required for that signal during a normal read mode operation. As a consequence, when the apparatus changed to a normal read mode operation, there was a sudden shift of the common mode voltage output signal from its relatively low value upward to the required level (commonly set by industry standards on a device-type basis) for normal read mode operations. This sudden shift was manifested in significant perturbations that required settling or damping before reliable information could be gleaned from the signal. The resulting unnecessary delays in response times in reading information conveyed by the output signals involved with the common mode output read signals adversely affected product performance.
Some industry specifications require that a read signal be provided for a hard disk drive product at a predetermined common mode voltage at a predetermined current drive, often at a current drive of approximately 5 ma (milliamps). Prior art preamp reader devices commonly draw approximately 12 ma-15 ma in order to reliably provide the required industry standard 5 ma signal at an output locus. It is inefficient to require a similar level of power consumption in a non-read mode. However, it is necessary (as discussed above) to maintain the output common mode voltage signal at a substantially constant level in such non-read modes of operation. This has been another problem in apparatuses configured according to the prior art.
There is a need for a common mode voltage signal apparatus configured for providing information contained in an input signal for use by an information processing device that can keep the common mode output voltage signal level substantially constant in various operational modes.
There is also a need for a common mode voltage signal apparatus configured for providing information contained in an input signal for use by an information processing device that can consume less power during non-read modes of operation while keeping the common mode output voltage signal level substantially constant.
The present invention solves both dilemmas—lower power consumption during non-read modes of operation while keeping the common mode output voltage signal level substantially constant. The preferred embodiment of the apparatus of the present invention can reliably provide a level-voltage signal at an output locus of a preamp reader device in a non-read mode while drawing less than 1 ma.